Pyrethroid-resistance in Anopheles gambiae s.l (Culicidae) populations from the Sudan Savannah ecoregion in Nigeria is partly mediated by knockdown mutation

Abstract

OBJECTIVE: Anopheles gambiae s.l. is the major malaria vector in sub-Saharan Africa, and increasing pyrethroid resistance threatens vector control. This study investigated the prevalence of knockdown resistance (kdr) mutations and pyrethroid susceptibility in An. gambiae s.l. populations from Kwara State, North-Central Nigeria. RESULTS: A total of 250 An. gambiae s.l. mosquitoes were collected from three Local Government Areas. Molecular analysis identified An. coluzzii (31.2%, 95% CI: 25.7-37.3%), An. gambiae s.s. (16.8%, 95% CI: 12.6-22.0%), and An. arabiensis (13.6%, 95% CI: 9.9-18.4%), while 38.4% failed amplification. All populations were resistant to permethrin, deltamethrin, and alphacypermethrin (mortality < 90%), with mortality ranging from 23% to 64% across locations. Knockdown times were fastest with deltamethrin (KDT₅₀: 32.75-52.80 min) and slowest with permethrin (KDT₅₀: 39.41-93.34 min). Kdr genotyping showed 41.6% homozygous resistant (RR) and 58.4% homozygous susceptible (rr) mosquitoes; no heterozygotes were detected. These findings indicate widespread pyrethroid resistance partially mediated by kdr mutations, with significant variation among locations and sibling species. The absence of heterozygotes suggests strong selection pressure, emphasizing the need for resistance monitoring and strategic vector control interventions.